Digital Coding of Color Video Signals--A Review

Abstract

This paper reviews the field of the efficient coding of color television signals. Because this paper is perhaps the first review on this topic, some background is given in the areas of colorimetry, visual perception of color and color television systems. We assume thaf the reader has some familiarity with luminance encoding techniques.Coding techniques themselves are divided into two broad groups: component coding methods in which each component (usually three) is coded separately, and composite coding methods in which the composite television signal with its "color" modulated subcarrier is processed as a single entity. Both approaches are covered in detail.The field is still growing, pushed primarily by the desire in the television area to find digital coding standards accepted by both broadcasters and carriers and suitable for use with NTSC, PAL and SECAM television systems.We discuss this aspect by comparing composite and component coding methods.

Digital color imaging

“…When these CMF's were first defined, calculations were typically performed on desk calculators, and the repetitive summing and differencing due to the negative lobes of the CIE RGB CMF's was prone to errors. Hence, the transformation from the CIE RGB CMF's to CIE XYZ CMF's was determined so as to avoid negative values at all wavelengths [42]. Since an infinite number of transformations can be defined in order to meet this nonnegativity requirement, additional criteria were used in the choice of the CMF's [43], [44, p. 531].…”

“…This was also recognized in early work with color television, and other color spaces were investigated. A review of this work is given in [42]. There are a few important points about this early work that are worth noting here.…”

Generating antialiased images at low sampling densities

“…Because green-sensitive cone cells are far more common in the human retina (and thus green is sampled more densely), sensitivity to green-colored noise is twice as great as to red-colored noise and four times greater than to blue-colored noise. This knowledge has been used in the encoding of color television transmission to make the most economical use of bandwidth [LIM77]. Figure 7 shows an image generated by a prototype antialiasing module combined with a basic ray tracer.…”

“…The approach has been to consider the perception of noise and operate near its threshold. While perception of noise is a complex subject, basic facts learned from work in color-television encoding and image noise measurement can be applied to this problem [LIM77,SAK77].…”

Region-Based Coding of Color Images Using Karhunen–Loeve Transform

“…One, we use ferential pulse code modulation (DPCM) [25], transform clustering or segmentation procedures to determine self-similar coding [25, 30], and vector quantization [12], developed image regions. Two, for each such region we use a Karhunen-initially for encoding monochrome images.…”